1. Field of the Invention
The present invention generally relates to a brake apparatus and, more particularly, to a brake apparatus having a brake pedal provided in a leg space of a vehicle to transfer a pressing force applied to the brake pedal to a master cylinder.
2. Description of the Related Art
A foot operated brake apparatus having a brake pedal for inputting a force by applying a foot press is disclosed in Japanese Laid-Open Patent Application No.6-211115. The brake apparatus disclosed therein has a function to prevent a displacement of a brake pedal when a force is applied from a frontal direction such as when the front of the vehicle is involved in an accident. In this brake apparatus, the brake pedal supported by a pedal support is connected to a master cylinder via a booster so that the master cylinder generates an appropriate hydraulic pressure in accordance with a pressing force applied to the brake pedal by an operator. The booster is provided for increasing the pressing force applied to the brake pedal. The booster and the brake support are mounted on a cowl provided above the brake pedal. More specifically, the brake support is fixed to the cowl by bolts fastened to slits formed in the cowl. The slits are elongated in a front-to-rear direction of the vehicle so that the brake support slides in the rear direction and causes downward movement of the brake pedal. This arrangement prevents transmission of a force exerted on the brake apparatus when the vehicle crushes in the front.
In this type of brake apparatus, a link mechanism is provided to transmit a force applied to the brake pedal to the master cylinder. The link mechanism comprises a brake pedal including a lever portion and a push rod as an input shaft of the master cylinder. More specifically, the brake pedal is supported by a pedal support directly under the cowl, and the push rod is connected in the middle of the lever portion of the brake. In this construction, a desired lever ratio required for the link mechanism can be easily achieved. Thus, a good brake feel can be obtained.
Accordingly, in the conventional brake apparatus, generally the pedal support is extended upwardly from a position of the booster to a dash panel. This is a reason for mounting the booster and the brake pedal on the cowl in the above-mentioned brake apparatus.
However, in the above-mentioned construction in which the brake pedal is supported under the cowl and the link mechanism is constituted by the brake pedal and the push rod, the booster must be spaced apart from the brake pedal in the front-to-rear direction of the vehicle.
When the brake apparatus is mounted on the vehicle, the position of the pedal is determined first in view of operability of the brake pedal. Positions of other component parts including the booster are determined by reference to the position of the brake pedal. Accordingly, the position of the booster is moved further toward the front of the vehicle as the distance between the booster and the brake pedal is increased. As a result, space between the booster and an engine positioned in front of the booster is reduced. This space is hereinafter referred to as a crush space. From this point of view, the above-mentioned conventional brake apparatus has a problem in that it is difficult to provide a sufficient crush space in front of the booster.
Generally, the booster is provided in a disk brake apparatus so as to increase a pressing force applied by a driver since a self servo effect cannot be obtained in the disk brake apparatus. In the booster of this type, a servo ratio is important. Japanese Laid-Open Utility Model Application No.4-35962 discloses a structure in which the servo ratio is changed during a brake applying operation.
FIG. 1 shows a booster disclosed in the above-mentioned document. As shown in FIG. 1, a power piston 108 is situated in a space formed between a front shell 100 and a rear shell 102 in a state where the power piston 108 is urged by a return spring 110. The power piston 108 comprises a valve body 104 and a diaphragm plate 106. A diaphragm 112 is provided on a back face of the diaphragm plate 106 so as to divide the space within the shells into a negative pressure chamber 114 and an atmospheric pressure chamber 116.
An operating rod 118, a plunger 120, a reaction disk 122 and a push rod 124 are provided, in that order from the rear end, along the center axis of the power piston 108. A predetermined gap is formed between the reaction disk and a pressing portion 120A formed on a front end of the plunger 120. An atmospheric pressure valve 120B is formed on the rear end of the plunger 120. A vacuum valve 130A of a poppet valve 130 is pressed by a return spring 128. An end of a negative pressure passage 132 is open in the vicinity of the vacuum valve 130A of the poppet 130. An atmospheric pressure passage 134 is formed in the vicinity of the atmospheric pressure valve 120B of the plunger 120.
Additionally, a reaction disk 122 comprises a first reaction disk 122A and a second reaction disk 122B. The first reaction disk 122A has a convex shaped cross section and is positioned on the push rod 124 side. The second reaction disk 122B has a ring shape and is positioned on the back side of the first reaction disk 122A The hardness of the first reaction disk 122A is lower than that of the second reaction disk 122B.
In the above-mentioned structure, when a pressing force is applied to the brake pedal, a periphery of the second disk is pressed by a cylindrical portion 104A of the valve body 104. Thus, the first reaction disk 122A having a lower hardness is deformed toward the plunger 120, and contacts the pressing portion 120A of the plunger 120. Accordingly, a servo ratio at this stage is represented by tan "THgr"1 as shown by a line A-B in the graph of FIG. 2. When the pressing force applied to the brake pedal is increased, the second reaction disk 122B also contacts the pressing portion 120A of the plunger 120. Thus, the servo ratio at this stage is represented by tan "THgr"2 as shown by a line B-C in the graph of FIG. 2. When the pressing force is further increased, the servo ratio is changed to a value represented by tan "THgr"3 as shown by a continuing line C in the graph of FIG. 2. Accordingly, in the above-mentioned structure, the servo ratio can be changed during operation of the booster.
However, in the above-mentioned structure, the characteristic (a booster characteristic) of the booster exhibits an upwardly closed convex characteristic curve. That is, the servo ratio is decreased as the pressing force is increased. Generally, a brake pad has the same characteristic and exhibits an upwardly closed convex characteristic curve. Thus, the braking characteristics (a pressing force versus deceleration characteristic) also exhibit an upwardly closed convex characteristic curve when the two characteristics are combined. This has a disadvantage in that brake pedal operation feel deteriorates.
Japanese Laid-Open Patent Application No5-185912 discloses a brake apparatus having a lever ratio changing mechanism provided between a brake pedal and an output member connected to a brake booster. The lever ratio changing mechanism changes a lever ratio of the entire brake pedal mechanism. More specifically, the lever ratio changing mechanism gradually increases the lever ratio as the brake pedal moves from an initial position to a start braking position, and gradually decreases the lever ratio as the brake pedal moves from the brake start position to the end of the brake pedal stroke.
Accordingly, when the brake pedal is on the way to the start braking position, that is, when the brake pedal is in an idling range (may be referred to as a first fill range), the lever ratio is small. Thus, the travel of the output member connected to the brake booster is large relative to travel of the brake pedal. This results in a completion of the first fill by a short stroke of the brake pedal. Additionally, since a change in pressing force transmitted to the brake booster per unit stroke is decreased, a fine control of deceleration can be obtained. Especially, when the brake pedal is pressed strongly, a rigid brake operation feel is achieved since the lever ratio is decreased toward the end of the brake pedal stroke. This improves the feel of a brake operation.
The above-mentioned document also teaches that it is desirable to increase a servo ratio of the brake booster so as to prevent an increase in a required pressing force to the brake pedal due to a decrease in the lever ratio in a strong braking range, that is, when the brake pedal is pressed strongly.
Thus, in the brake apparatus of the above-mentioned document, the servo ratio of the brake booster is increased when the magnitude of braking is shifted from a normal braking range to the strong braking range. This generates discontinuity in a characteristic change between a changing rate of a brake pressing force and a deceleration rate of the vehicle at a point where the pressing force is shifted between the normal braking range and the strong braking range.
The characteristic relationship between a changing rate of a brake pressing force and deceleration rate of the vehicle is equivalent to the characteristic relationship between a brake effect and the pressing force applied to the brake pedal. Accordingly, in the conventional brake apparatus, a driver has a feeling that a brake effect in the normal braking range is greatly different from that in the strong braking range. This causes a problem in that a poor braking operation feeling is conveyed to a drive.
It is a general object of the present invention to provide an improved and useful brake apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a brake apparatus in which a lever ratio of a brake pedal can be set to a desired ratio even when the brake lever is positioned adjacent to a brake booster.
Another object of the present invention is to provide a brake apparatus having a brake booster providing a good brake operation feeling by constructing the brake booster to have an optimum servo ratio changing characteristic.
Another object of the present invention is to provide a brake apparatus having a good brake feel operation provided by a combination of a link mechanism of a brake pedal having a lever ratio changing mechanism and a brake booster increasing a pressing force input to the link mechanism.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a brake apparatus for a vehicle comprising a link mechanism and a power generating unit generating a hydraulic pressure to each wheel of the vehicle, the link mechanism comprising:
a brake pedal including a lever portion having a first end and a second end, a pedal provided on the first end, the lever portion being pivotally supported at a pivot point between the first and second ends;
a pivot link having a first end and second end, the second end of the pivot link connected to a force transmission member connected to the power generating unit, the pivot link being pivotally supported at a pivot point between the first and second ends of the pivot link; and
a connection link having a first end and a second end, the first end of the connection link connected to the second end of the lever portion of the brake pedal, the second end of the connection link connected to the first end of the pivot link,
wherein travel of the pedal of the brake pedal is transmitted to the force transmission member via the connection link so that a lever ratio of the link mechanism is changed while the pedal travels from an initial position to a stroke end position, the lever ratio defined as a ratio of a rate of change in movement of the pedal to a rate of change in movement of the force transmission member.
According to this invention, when a pressing force is applied to the brake pedal, the brake pedal pivots about the pivot points. Thus the pressing force is transmitted to the second end of the lever portion in accordance with the lever ratio of the lever portion. The force transmitted to the second end of the lever portion is transmitted to the pivot link via the connection link. The pivot link transmits the force to the force transmitting member by pivoting in accordance with the lever ratio of the pivot link.
The lever ratio of the link mechanism as a whole is determined by a geometrical arrangement of the brake pedal, the connection link and the pivot link. Thus, a desired lever ratio of the link mechanism can be established with a relatively high freedom of design. This provides a desired lever ratio with a relatively small distance in the front-to-rear direction between the brake pedal and the force transmitting member.
In the above-mentioned invention, the lever portion of the brake pedal may be supported by a pivot shaft mounted on a pedal support fixed to a stationary member of the vehicle, the pedal support having a first end extending to a position below the pivot shaft.
In this construction, when the pivot shaft of the brake pedal is moved rearwardly for some reason such as providing a front crush zone of the vehicle, the pedal support pivots about the first end of the pedal support. Thus, the brake pedal moves substantially downward in the vehicle. This prevents the pedal from protruding toward the interior of the passenger compartment.
Additionally, the stationary member may separate the engine compartment from the passenger compartment, the power generating unit may have a booster increasing a power input by the link mechanism, and the pedal support may have a second end opposite to the first end of the pedal support extending to a position below the pivot shaft, the second end of the pedal support fixed to the booster.
This construction permits the link mechanism being mounted to the booster together with the pedal support before the booster is mounted on the vehicle. Thus, the assembling of the brake apparatus can be simplified, and an adjustment of a position of the brake pedal can be performed before it is mounted on the vehicle.
Additionally, there is provided according to another aspect of the present invention a brake apparatus for a vehicle comprising a link mechanism and a power generating unit generating a hydraulic pressure to each wheel of the vehicle, a brake booster being provided between the link mechanism and the power generating unit to increase an input force input from the link mechanism to the power generating unit by operation of negative pressure generated in an air intake system of an engine provided in the vehicle, the brake booster comprising:
an operating rod connected to the link mechanism so that the input force is input from the link mechanism;
a push rod connected to the power generating unit to provide an output force to the power generating unit, the output force being generated by increasing the input force; and
increasing means, provided between the operating rod and the push rod, for increasing a rate of increase of the output force so that the rate of increase is increased as the input force is increased.
According to this invention, since the rate of increase in the output of the booster is increased as the input force to the booster is increased, a servo ratio of the booster can be increased in a region in which effectiveness of the braking is decreased due to a normal characteristic of a brake pad. Accordingly, the relationship between the deceleration by the braking operation and the pressing force input to the brake pedal can be set to a substantially linear relationship. Thus, the brake apparatus according to this invention can provide a good brake feeling in which effectiveness of braking is not decreased during a strong braking operation.
In one embodiment of the present invention, the increasing means may comprise an elastic reaction disk engaging the push rod and a plunger engaging the operating rod, the reaction disk being pressed by an end of the plunger when the input force is supplied, a space being formed around the end of the plunger, the reaction disk protruding into the space when the reaction disk is pressed by the end of the plunger.
Accordingly, a part of the force transmitted from the operating rod to the push rod via the plunger and the reaction disk is absorbed by an elastic deformation of the reaction disk permitted in the space formed around the end of the plunger. The force is directly transmitted when the space is completely filled with the deformed reaction disk. Thus, the servo ratio is increased as the deformation of the reaction disk is increased, that is, the force input to the operating rod is increased. Accordingly, the brake apparatus according to this invention can provide a brake feeling in which effectiveness of braking is not decreased even when the brake pedal is pressed almost to the end of its stroke.
In one embodiment of the present invention, the space may be formed by a recess having a bottom surface substantially parallel to a surface of the reaction disk, the bottom surface being a predetermined distance apart from the surface of the reaction disk. In an alterative case, the space may be formed by a recess having a bottom surface having a taper extending toward the plunger.
Additionally, there is provided according to another aspect of the present invention a brake apparatus for a vehicle, comprising a link mechanism and a power generating unit generating a hydraulic pressure to each wheel of the vehicle, a pressing force being input through the link mechanism, a brake booster being provided between the link mechanism and the power generating unit to increase an input force input from the link mechanism to the power generating unit by operation of negative pressure generated in an air intake system of an engine provided in the vehicle, wherein
the link mechanism comprises lever ratio changing means for changing a lever ratio of the link mechanism so that the lever ratio is gradually decreased as a pedal stroke is increased after the pedal stroke reaches a predetermined point, and
the brake booster comprises increasing means for increasing a rate of increase of the output force so that the rate of increase is increased as the input force is increased, and
wherein a brake characteristic of the brake apparatus is a linear relationship relative to the deceleration of the vehicle, the brake characteristic being defined as an inclination of the deceleration with respect to the pressing force input to the link mechanism.
In this invention, since the link mechanism gradually decreases the lever ratio, a change in the brake force per unit stroke of the brake pedal during a medium braking operation can be set small, resulting in a fine control of the brake force. On the other hand, during a strong braking operation, a sufficiently rigid feeling can be obtained due to a gradual decrease in the lever ratio in the medium braking region to the strong braking region.
However, according to the above-mentioned action of the link mechanism, a pressing force required during the strong braking operation is increased because the lever ratio is decreased. In this invention, this disadvantage is compensated by increasing the servo ratio of the brake by the booster having means for increasing the rate of increase of the output force especially during the strong braking operation. That is, in this invention, the link mechanism and the brake booster are appropriately combined so that a brake characteristic of the brake apparatus as a whole exhibits a constant or a linearly increasing relationship relative to the deceleration of the vehicle. This provides for an improved brake feel.
In one embodiment, the link mechanism may comprise:
a brake pedal including a lever portion having a first end and a second end, a pedal provided on the first end, the lever portion being pivotally supported at a pivot point between the first and second ends;
a pivot link having a first end and second end, the second end of the pivot link connected to a force transmission member connected to the power generating unit, the pivot link being pivotally supported at a pivot point between the first and second ends of the pivot link; and
a connection link having a first end and a second end, the first end of the connection link connected to the second end of the lever portion of the brake pedal, the second end of the connection link connected to the first end of the pivot link,
wherein travel of the pedal of the brake pedal is transmitted to the force transmission member via the connection link so that a lever ratio of the link mechanism is changed while the pedal travels from an initial position to a stroke end position, the lever ratio defined as a ratio of a rate of change in movement of the pedal to a rate of change in movement of the force transmission member, and
the brake booster may comprise:
an operating rod connected to the link mechanism so that the input force is input from the link mechanism;
a push rod connected to the power generating unit to output the output force to the power generating unit, the output force being generated by increasing the input force: and
an elastic reaction disk engaging the push rod and a plunger engaging the operating rod, the reaction disk being pressed by an end of the plunger when the input force is supplied, a space being formed around the end of the plunger, the reaction disk protruding into the space when the reaction disk is pressed by the end of the plunger, the space being formed by a recess having a bottom surface with a taper toward the plunger.
In another embodiment, the link mechanism may comprise:
a brake pedal including a lever portion having a first end and a second end, a pedal provided on the first end, the lever portion being pivotally supported at a pivot point between the first and second ends;
a pivot link having a first end and second end, the second end of the pivot link connected to a force transmission member connected to the power generating unit, the pivot link being pivotally supported at a pivot point between the first and second ends of the pivot link; and
a roller rotatably supported at the first end of the pivot link, the roller engaging a surface of the lever portion of the brake pedal between the second end and the pivot point of the brake pedal,
wherein travel of the pedal of the brake pedal is transmitted to the force transmission member via the roller and the pivot link so that a lever ratio of the link mechanism is changed while the pedal travels from an initial position to a stroke end position, the lever ratio defined as a ratio of a rate of change in movement of the pedal to a rate of change in movement of the force transmission member.
Additionally, the brake booster may comprise:
an operating rod connected to the link mechanism so that the input force is input from the link mechanism;
a push rod connected to the power generating unit to output the output force to the power generating unit, the output force being generated by increasing the input force: and
an elastic reaction disk engaging the push rod and a plunger engaging the operating rod, the reaction disk being pressed by an end of the plunger when the input force is supplied, a space being formed around the end of the plunger, the reaction disk protruding into the space when the reaction disk is pressed by the end of the plunger, the space being formed by a recess having a bottom surface with a taper toward the plunger, the end of the plunger having a tapered surface.
In this embodiment, a desired servo ratio can be obtained by appropriately changing a taper angle of the end of the plunger.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.